Population - the number of a particular species in an area at a specific time

Habitat - the area in which an organism lives

Ecosystem - a natural unit of living and non-living parts that interact to produce a stable system in which the exchange of materials between living and non-living parts cycles

Biome - A biome is a large, easily differentiated community unit arising as a result of complex interactions of climate, other physical factors and biotic factors. Examples of Biomes are tundra, temperate grassland, desert and tropical rainforest.

Biosphere - The Biosphere is the collective interaction of all the biomes on the Earth.

RELATIONSHIPS IN THE ENVIRONMENT

Symbiosis - a relationship in which two organisms of different species 'live together' for a period of time

Parasitism - a form of symbiosis in which one organism derives nutrients from the second organism which suffers some harm but is usually not killed (e.g. A tick is the parasite that feeds off a dog which is the host.)

Mutualism - a form of symbiosis in which both organisms help each other (e.g. A remora fish eats the algae and barnacles from the skin of a shark which, in turn, protects the remora.)

Commensalism - a form of symbiosis in which one organism helps the other organism, but there is no benefit nor harm done in return (e.g. A clown fish lives inside a sea anemone and is protected by it. The sea anemone derives no benefit nor harm from the relationship.)